Explosive composition and method of producing same



Patented Mar. 21, 1944 EXPLOSIVE COMPOSITION AND METHOD OF PRODUCINGSAME Sterling B. Watt and Norman W. Adolph, Grafton, Ill., assignors toIllinois Powder Manufacturing Company, St. Louis, Mo., a corporation ofIllinois No Drawing. Application June 14, 1940, Serial No. 340,598

4 Claims.

Our invention consists in a new and useful improvement in explosivecomposition and method of producing same and is particularly designed toproduce a novel form of composition which is characterized by extremelylow sensitizer content and high sensitivity to detonation. This char-'acter of our improved composition is due both to the nature of thecomposition and the method of its production. Our improved compositionis suitable for all types of blasting and is peculiarly valuable for usein certain types of mining requiring the use of explosives having thespecial characteristics possessed by our improved composition. Theparticularly novel and valuable feature of our invention is the materialreduction of the proportion of sensitizers in our coinposition, byreason of the use of a very small proportion of aluminum powder, and thenovel method of producing our composition hereinafter fully disclosed.

Ammonium nitrate compositions containing low contents of sensitizershave long been in use. But these compositions have been characterized bysuch low sensitivity that their application has been greatly restricted.For example, free-running dynamites, packed in bags, are poured intorelatively large diameter bore holes of the well drill type, or pouredinto the cavity produced by springing a small diameter bore hole with apreparatory charge of more sensitive dynamite. The

column of explosives is never of small diameter or cross-section at anypoint. The recommended practice in the use of this type has'been toinitiate detonation by means of a cartridge or cartridges of highlysensitive type, such as standard 40% N. G. or 40% ammonia dynamites.Permissible ammonium nitrate compositions containing low contents ofsensitizers have been used in mining coal. The minimum recommendeddiameter of the most desirable type has been set at 1%". In spite ofthis recommendation, however, some have been used in 1 /2" or even 1%"diameters. A great deal of trouble, due to unexploded cartridges byreason of insensitivity of the compositions, has been experienced in allthe sizes used. Our invention is an improvement in such compositions andmethod of production, whereby the content of sensitizers is greatlreduced, and yet the composition possesses a high degree of sensitivity.

There has long been a demand from users of explosives for non-headachecausing explosive compositions. This characteristic is one of thestrongest sales arguments for explosive compositions of the nitro-starchtype. The compositions of our invention contain such small quantities ofsensitizers capable of causing headaches in workers handling them, andthe headache causing sensitizers are applied in such a man ner, thatwhile they can not be described as strict- 1y non-headache causingcompositions, they are materially improved in this respect.

Our compositions may be prepared in strengths from 20% to 65%. We givebelow examples of our compositions in approximately 40%,'50% and 60%strengths:

N itroglycerin 3. 00 4. 00 5. 00 Dry nitrocotton 05 05 05 Ammoniumnitrate 87. 50 73. 00 60.00 Sodium nitrate 2. 00 12. 50 20.00 Cornstarch5. 50 6. 00 5. 00 Sulphur 2. 50 8.00 Aluminum l. 00 1. 00 l. 00 Calciumcarbonate 95 95 95 If the above described compositions should beprepared according to the methods ordinarily used in explosive plants,viz., placing the dry ingredients in the mix bowl, followed by theliquid explosive, compositions of a low degree of sensitivity, lackingthe ability to bridge an air gap in the halved cartridge method, or atbest a gap of a few inches, would be produced.

If, however, the ammonium nitrate and the sodium nitrate are placed inthe mix bowl, the nitroglycerin and nitrocotton are gelled separate- 1yfor three minutes in a suitable container and then poured into themixbowl, and mixing is performed for three minutes, then the remaininingredients, except the aluminum, are added, and mixing continued foranother three minutes, after which the aluminum is added andincorporated for three minutes, compositions of high sensitivity areproduced. The composition, according to the 60% formula, thus produced,possesses sensitivity to detonation of 14" by the halved cartridgemethod; similarly the composition according to the 50% formula asensitivity of 16", and the composition according to the 40% formulaNitroglycerin Dry nitrocotton.

Ammonium nitra Sodium nitrate- Cornstarch 2. -1. 50 3. 50 Ivory meal3.00 4. 50 Sulphur 2.00 7.50 Regranulated cor 2.00 1. 50 Aluminum 1.001.00 Calcium carbonate 95 95 .95

Using the method above described for the previous examples, thefollowing sensitivity and stick counts in 1 x 8" size per 50 lbs. wereobtained: 60%, 16",142 sticks; 50%,16", 143 sticks; 12", 137 sticks.Again the tests refer to the halved cartridge method in IA'x 8" size.

The characteristics of our compositions may be further varied by usingammonium nitrates of different degrees of coarseness. In the aboveexamples, ammonium nitrate of fairly fine grain was used. Rates ofdetonation were, in the first set of formulae: 60%, 6,320 ft./sec.;6,610

ft./sec.; 40%, 7,710 ft./sec.; in the second set of formulae: 7,200ft./sec.; 50%, 7,650 ft./sec.; 40%, 7,440 ft./sec. These rates weredetermined by the DAutriche method. The rates of detonation ma be variedover a fairly wide range by suitable formula changes.

By using extremely coarse ammonium nitrate, compositions exhibiting lowrates of detonation and high degrees of sensitivity may be obtained.

For example:

Nitroglycerin 3. 00 3. 00 3. 00 Nitrocotton 05 .05 05 Coarse ammoniumnitrate 89. 00 89.00 86. Sodium nitrate 2. 50 2.00 3. 25 Cornstarch"- l00 1.00 l 75 Fine sawdust"- 2 00 2.50 2 25 Aluminunn l 50 l. 50 2 00Calcium carbonate 95 95 Sensitivity .1 12 12 7 14 Rate of detonation 4,380 ft./sec. 4, 243 ftJsec. 4, 656 it./sec. Stick count, 1% x 8/50 lbs140 136 Thus, by using extremely low amounts of sensitizers and ourimproved method of production, using coarse ammonium nitrate, we haveobtained highly sensitive compositions of sur prisingly low rate ofdetonation. Heretofore, rates of detonation in the neighborhood of 6,000ft./sec. have been considered very low; and at the same timecompositions having such rates have possessed low sensitivity.

It is obvious from the foregoing that our invention makes it possible tofurnish the coal mining industry with explosive compositions which aresafe in the presence of dusty or gaseous atmospheres, and which will becapable of producing large lumps of coal with a minimum of fines,without the difficulty of unexploded cartridges.

We have used the term nitroglycerin in the sense of liquid explosive. Itincludes mixtures of glycerin tri-nitrate and ethylene glycol dinitrate,mixtures of glycerin tri-nitrate, ethylene elvcol (ii-nitrate andnitroaromatic compounds and/0r nitro-parafline, nitro-sugars and thelike.

We may also find it advantageous to use other oxidizers replacing sodiumnitrate. The nitrates of the other alkali metals and those of the heavymetals may be employed. Similarly, olorates and perchlorates may be usedinstead of sodium nitrate. I

The types of carbonaceous materials used in the foregoing examples arenot to be considered limiting. To impart the desired characteristics forspecific blasting conditions, we may employ comminuted apricot meal,almond meal, rice hulls, wood flour and the like. In place of wood pulp,we may employ mallow pith, bagasse, ex- .panded cereals, and the like.

We have used finely powdered aluminum in our compositions, butrelatively coarser particles of aluminum, such as turnings, filing, etc.may be used. We have used percentages of aluminum ranging from 1% to 8%.In our more desirable compositions we have found from 1% to 3% to besatisfactory. We do not wish to be limited as to the amounts of aluminumwe employ. It is to be understood that the mechanism of the detonationdepends on the particles of aluminum transmitting the wave of detonationthrough the inert materials to the sensitized grains of ammonium nitrateand sodium nitrate. The particles of aluminum have such covering powerthat some of them adhere to the already sensitized grains. It is notnecessary that both the ammonium nitrate and the sodium nitrate beplaced together in the mix bowl and the gelled explosive added thereto.In producing certain compositions, we find it advantageous to put onlythe ammonium nitrate in the bowl, add the gelled explosive, perform themixing thereof, and then add the sodium nitrate at a later stage of themixing process.

Having described our invention, what we claim 1. An explosivecomposition containing from 60% to 89% ammonium nitrate grains coatedwith a gelatinized explosive nitric ester, containing .05% nitrocottonto which particles of aluminum adhere, distributed throughout a matrixof sodium nitrate, .aluminum particles and inert material, the aluminumparticles being from 1% to 2%.

2. An explosive composition containing from 3% to 5% of a liquidexplosive nitric ester in which has been gelled .05% nitrocotton, theremainder of the explosive strength being engendered by from 60% to 89%ammonium nitrate grains, in which substantilly all the gelled liquidexplosive nitric ester is adhered to the ammonium nitrate grains whichare distributed throughout a matrix of from 2% to 20% sodium nitrate,inert materials and from 1% to 2% aluminum powder, said matrixcontaining substantially little gelled liquid explosive nitric ester.

3. The method of producing an explosive composition which consists inmixing from 60% to 89% of ammonium nitrate grains and from 3.05% to5.05% of a gelled liquid explosive nitric ester so as to coat the grainswith the explosive nitric ester; mixing the coated grains with from 2%to 20% of sodium nitrate grains and a quantity of inert material to forma matrix throughout which the ammonium nitrate grains are thoroughlydistributed; and adding from 1% to 2% of aluminum particles so that theyare distributed throughout said matrix and that certain of saidparticles adhere to the ammonium nitrate grains.

4. The method of producing an explosive composition so as to impartthereto a high degree of sensitivity, which consists in mixing from 60%to 89% of ammonium nitrate grains and from 3.05% to 5.05% of a gelledliquid explosive nitric ester, so as to coat the grains with theexplosive nitric ester; mixing the coated grains with from 2% to 20% ofsodium nitrate grains and a quantity of inert material to form a matrixthroughout. which the ammonium nitrate grains are thoroughlydistributed; andadding from 1% to 2% of aluminum particles so that theyare dis- 5 tributed throughout said matrix.

STERLING B. WATT.- NORMAN W. ADOLPH.

